Polygon Affordability Index (PAI) scores each geography 0 to 100 — higher means more affordable. The score is a weighted composite of three burden measures, all drawn from actual HMDA transactions: Payment Burden (50%) — monthly mortgage payment as a percentage of applicant income. Price Burden (30%) — property value relative to annual income, indicating years of salary needed to buy. Down Payment Burden (20%) — down payment required as a percentage of annual income, capturing the entry barrier that payment-only measures miss. To ensure consistency across all geographies and years, PAI applies a standard filter set: purchase loans, fixed rate, closed-end, 1–4 family, originated loans only. No refinances, no adjustable rate products, no unresolved applications — just actual home purchase transactions.